A typical Power over Ethernet (PoE) power communications system includes power-sourcing equipment (PSE) and a set of remotely-powered network devices (e.g., PDs or Powered Devices) that connect to the power-sourcing equipment through network cables. Power-sourcing equipment can include i) power supply circuitry to provide power through a cable to a respective network device and ii) transmit/receive circuitry to support data communications with a respective network device at the other end of a cable. Accordingly, when supplied power through the cable, a user of the respective network device is not burdened with having to separately connect his network devices to another power source such as a 115 volt wall outlet. Instead, the network device coupled to a port of the power-sourcing communications equipment relies on power received through the cable.
There are industry standards which attempt to provide guidelines for manufacturing certain types of power-sourcing communications equipment. For example, the IEEE 802.3af standard, which is also called the “Power over Ethernet” standard, defines ways to build Ethernet power-sourcing equipment and powered devices. In particular, the IEEE 802.3af standard identifies ways to deliver certain electrical features (e.g., 48 volts) of DC power over unshielded twisted-pair wiring (e.g., Category 3, 5, 5e or 6 network cables, patch cables, patch-panels, outlets and connecting hardware) to a variety of Ethernet devices such as IP phones, wireless LAN access points, laptop computers, web cameras, and the like.
In the context of the IEEE 802.3 Ethernet Standard, which does not cover UPS applications and is limited to PSE and PD interactions, the power-sourcing equipment discussed above is referred to a Power Sourcing Equipment (PSE) and network devices coupling to the PSE (e.g., a switch device) through cables are known as Powered Devices (PDs).
Power-over-Ethernet offers benefits in simplifying deployment of small data devices because remote power supplies are eliminated. Power-Sourcing Equipment may be Endpoint, when integrated into an Ethernet switch, or Midspan, when inserted between a non-PoE Ethernet switch and a PD. A PSE may employ Alternative A, wherein power is conveyed over pairs 1 and 4, or Alternative B, wherein power is conveyed over pairs 2 and 3. Endpoint PSEs using Alternative A may use Normal or Inverted polarity. PoE devices may conform to the IEEE 802.3af standard, may be proprietary, or may be compatible with the standard but still operate with proprietary devices. The various PSE configurations require a test instrument with considerable flexibility in wiring configurations.
Because testing of PoE-enabled Ethernet switches should include both data testing and PSE testing, one capability is the inclusion of data and PSE testing in a single instrument. Such a device could be realized by combining the PoE instrumentation concepts herein with well-known data-testing techniques. However, because of the very large installed base of data-testing instrumentation, an attractive capability is presented by realization of a PSE tester which can be transparently inserted between an Ethernet switch and a data-only tester. A stand-alone PSE test capability would enable existing data-testing suites to be upgraded for PSE testing. Notwithstanding this, the techniques described herein for a stand-alone PSE-testing capability are further applicable to make an integrated PSE-testing/data-testing instrument.
An instrument useful for parametric production testing as well as laboratory design verification and characterization should support a wide variety of tests, provide high accuracy measurements, and enable a wide range of parameter variations. In addition, such an instrument should be easily interfaced to computers for control and analysis of data, readily incorporated into test configurations with other equipment, and provide a rich set of primitives to support a flexible scripting language and/or GUI interface.